feat(signup): community guidelines agreement and policies routes

Introduces /community-guidelines and /policies/{privacy,terms,[slug]} pages,
swaps the signup/invite checkbox from agreedToTerms to agreedToGuidelines,
adds Member.agreement.acceptedAt, and stamps the field when a Helcim
customer is created.

server/api/invite/accept.post.js

@@ -46,6 +46,7 @@ export default defineEventHandler(async (event) => {
     contributionTier: body.contributionTier,
     bio: body.motivation || undefined,
     status: body.contributionTier === '0' ? 'active' : 'pending_payment',
+    agreement: { acceptedAt: new Date() },
   })
 
   await assignMemberNumber(member._id)